I highly doubt Kim K or any of the Kardashians for that matter are having sex for money unless it's some insane "offer I can't refuse" type of money. The money they've made and can still make is real. I know someone who personally paid Kendall 30k for a photoshoot [to promote a product he had] back in 2012. Mind you this is 2012 Kendall Jenner, she was only 16/17 years old and didn't have the modeling cache that she currently has. That same shoot today would probably be at least 5x that amount, likely ever more. So imagine what Kim is currently able to making?
I'm not saying she doesn't sleep with other people or doesn't have any weird sexual proclivities but if she is doing that it isn't for money.